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Fix a Cold End Clog and Take Apart the Ubis 13 Extruder

3D printers are prone to many technical problems, from filament jams clogs and bed adhesion problems to loose screws and messed-up firmware. One bane of 3D problems is the cold end clog. Here’s how to take apart the Ubis 13 hot end, found on the Printrbot Play and Printrbot Simple 3D printers, to clear the clog.

The Problem:

Your Ubis 13 cold end is clogged and filament remains stuck even if you try to retract it or if you load more filament.

If it takes a substantial amount of force to yank filament out of a cold printer, forcefully pulling the filament out may cause it to break within the extruder. Cold end clogs can be completely prevented by unloading filament only when the printer is at temp.

A cold end clog may also be caused by letting the heat sink get too hot by not turning the cooling fan on. The filament in the heat sink gets melty and may cool stuck to the inside of the heat sink.

Words of Warning:

If you take a part the hot end, it’ll never be the same again. Taking it apart breaks the ‘factory seal’ and there’s a chance you’ll have chronic leaking problems even if you put it together very tightly. So be wary.

Preliminary Measures to Try BEFORE You take the hot end apart:

There’s a couple things you can try if you have a cold end clog. First, if you think the clog may have been caused by the cold end becoming too hot and then cooling, remove all cooling fans and bring the hot end up to temp, and wait. Eventually the cold end will become hot enough that you might be able to push the filament clog through.

Another currently untested possibility is to get an 8” solid gauge (NOT stranded, otherwise pieces may break off inside your printer), uncoated copper wire that has a diameter slightly smaller than the filament, and a soldering iron. Wrap the wire around the soldering iron tip, and bring the iron to the lowest temp possible. Insert the wire into the cold end and apply light pressure. The goal is to melt the filament with the wire and push it through. Don’t leave the wire in too long as the soldering iron temp will quickly cause the filament to burn and harden, making it even harder to push through.

Time Needed:

This fix could take an hour or two, especially if you have to take apart the hot end multiple times. Do it all in one go, from taking it apart to testing it out.

What You’ll Need:

Adjustable wrench or a wrench that will fit the nozzle and heat sink ends (pliers may work by they’re harder to use and may scratch up the heat sink)

Needle-nosed pliers

A thick, pointy needle that won’t bend under pressure (for cleaning any screw-threads, may be unnecessary)

Various allen/hex wrenches (the ones that came with your Printrbot printer)

Heat sink compound (optional)

Piece of aluminum foil or other nonflammable work surface

Steps:

First “home” the machine. Move the extruder to the center of the x-axis and adjust the z-axis so that the hot end tip is an about an inch off of the bed. This will make the hot end easier to access later.

We have to remove the hot end from the printer so we can take it apart. With the 3D printer powered off, take the fan shroud off using the second smallest hex wrench by removing the two hex-bit screws on top. Disconnect the fans. Make sure you remember which fan plugged into which connector.

Now the extruder is exposed, and the hot end can be removed. Loosen both of the screws that pinch the hot end in place, and slide it downward and out. Keep the thermistor and power connected to the printer.

Now the extruder can be taken apart. First, remove the red sock. If it’s a little stuck because of leaked filament, slide the needle between the heat block and sock and wedge it off.

A word of warning before you continue: You’ll be using pliers and wrenches on and near the heat block. The thermistor and power wires that travel into the heat block are delicate and can be ripped off or otherwise damage if they’re yanked of scraped with tools, and are very difficult to replace. In addition, if a tiny bit of the metal inside the wires is exposed, you must be careful not to short a tool across them, or worse tear them off. You must be careful as you work near them!

Next, in your software, bring the hot end to temp it can be unscrewed. If you try to take the hot end apart while it’s cold, while possible, you risk damaging the parts or the internal threads. Bring it to the ideal temperature for the filament that’s stuck inside. Stick with 190°C if you’re using PLA plastic.

Grip the rubber end (the part farthest from the tip) of the hot end with the pair of large pliers. You’re going to unscrew the hot end metal tip first. Using either the adjustable wrench or the needle-nosed pliers, quickly unscrew the tip and set it on a piece of aluminum foil or other non-burnable material.

Quickly examine the hot end tip. If there’s any filament residue on the outside of the tip or on the threads, that’s an indication of chronic leaking problems. Use the sewing needle to scrape off any residual plastic on the outside while the tip is still hot. Be careful using the needle: the heat from the tip will conduct up the needle and may burn you.

Go back to the rest of the hot end. Still gripping the rubber cap with the pliers, examine the inside of the heat block. If you can see the clog up, try to pull or scrape the filament out.

The next step is to expose the heat break, which looks like a double-sided screw. Most likely the clog is within it. Use the needle-nosed pliers to unscrew the heat block, staying wary of the protruding. After the heat block is disconnected, it’ll be the only part of the hot end that’s being heated.

The heat break is still connected to the heat sink. Before disconnecting the two, identify where the clog is. Is it only in the heat break? First, using the smallest size hex wrench, loosen the setscrews in the bottom half of the heat sink. As it’s still hot, unscrew the other half of the heat break from the heat sink using pliers on the heat break and the wrench on the flat part of the heat sink. You’ll notice there’s whitish paste on the upper half of the heat sink. It’s heat sink compound that help conduct the heat from the heat block to the the heat sink.

Grip the heat break from the middle and stick the needle or copper wire through it to clear and filament. You’ll be able to tell right away if it’s clear. Be careful: again the heat will conduct quickly to the wire or needle.

With everything apart, turn off the power and let all the pieces cool. As they cool and are still warm, look for the clog and use the needle or copper wire to clear the clog. Make sure all screw threads are cleared of filament. You should be able to see clear though the heat sink, heat break, and heat block.

Once you’ve gotten all the pieces cleared, it’s time to screw it back together. You’ll have to use your muscles with this, as well as leverage from your tools. It needs to be tight, other wise you’ll get leakage that will clog the extruder again. If there was any residual filament on the screw threads, you should bring the heat block to temp so that the threads don’t grind while screwing. Start with the metal tip, and use pliers to tighten to the max. Replace the red sock on the heat break.

Then screw the heat break into the heat sink. If you have it, squirt some heat sink compound onto the heat break before you screw it in.

Screw the heat block and tip into the other half of the heat break. Use the adjustable wrench on the heat sink, and pliers on heat block. Tighten.

If your hot end is at temp, turn it off. Replace hot end back into the extruder, and tighten screws enough so the hot end won’t slip.

Reconnect the fans, and put the fan shroud back on.

Now it’s time to make sure everything’s fixed. Bring the hot end to temp. Choose a bright colored filament (if you have it) and load it into the extruder. A bright color will make it easier to troubleshoot in case there’s leaks.

Extrude the filament with you software, and verify that the plastic is coming through.

Try out a small print (how about the Maker Faire Bot?), and if it comes out successfully, you have fixed the clog! 😀

Note: When I fixed this problem with my hot end, I had to take it apart no less than four times before I got it screwed together tight enough.